Ebook ECG workout-Exercises in arrhythmia interpretation (6th edition): Part 2

(BQ) Part 2 book ECG workout-Exercises in arrhythmia interpretation presents the following contents: Ventricular arrhythmias and bundle-branch block, pacemakers, posttest. Invite you to consult.

9 Ventricular arrhythmias and bundle-branch block Overview The three preceding chapters have focused on supraventricular arrhythmias Supraventricular arrhythmias refer to those rhythms that originate above the bundle branches and include the sinus, atrial, and junctional rhythms The electrical impulse produced by supraventricular rhythms follows the normal conduction pathway, resulting in simultaneous depolarization of the right and left ventricles The resulting QRS complex is narrow (0.10 second or less in duration) Ventricular beats and rhythms (Figure 9-1) originate below the bundle of His in a pacemaker site in either the right or left ventricle When impulses arise in the ventricles, the impulse does not enter the normal conduction pathway, but travels from cell to cell through the myocardium, depolarizing the ventricles asynchronously Therefore, the ventricles are not stimulated simultaneously and the stimulus spreads through the ventricles in an aberrant manner, resulting in a wide QRS complex of 0.12 second or greater Since ventricular depolarization is abnormal, ventricular repolarization will also be abnormal, resulting in changes in the ST segments and T waves The ST segments and T waves will slope in the opposite direction from the main QRS deflection (if the ectopic QRS complex is predominantly negative, the ST segment is usually elevated and the T wave positive; if the ectopic QRS complex is predominantly positive, the ST segment is usually depressed and the T wave negative) A P wave is not produced in ventricular rhythms Ventricular arrhythmias include premature ventricular contractions (PVCs), ventricular tachycardia (VT), ventricular fibrillation (VF), idioventricular rhythm, accelerated idioventricular rhythm, and ventricular standstill All of these rhythms are associated with a wide QRS complex (except VF and ventricular standstill, which not have QRS complexes) Because the ventricles are the least efficient of the heart’s pacemakers, most of these rhythms are (or have the potential to be) life-threatening and demand prompt recognition and treatment The electrical impulse in bundle-branch block originates in the sinus node, not in ventricular tissue, but a discussion of bundle-branch block is included in this rhythm group because of the location of the block within the ventricles and the wide QRS complex Bundle-branch block The intraventricular conduction system consists of the right bundle branch and the left main bundle branch, which divides into two fascicles: an anterior fascicle and a posterior fascicle Block may occur in any part of this conduction system Normally, the electrical impulses travel through Figure 9-1 Ventricular arrhythmias and bundle-branch block 197 ECG workout_Chap09.indd 197 4/28/2011 5:41:16 AM 198 Ventricular arrhythmias and bundle-branch block the right bundle branch and the left bundle branch and its fascicles at the same time, causing simultaneous depolarization of the right and left ventricles, resulting in normal depolarization and a QRS duration of 0.10 second or less When one of the bundle branches is blocked, the electrical impulse travels down the intact bundle, depolarizing that ventricle first, then the impulse progresses through the interventricular septum to depolarize the other ventricle Depolarization of one ventricle before the other is called sequential depolarization Depolarization of the ventricles is delayed, resulting in a wide QRS complex of 0.12 second or greater The presence of a bundle-branch block (Figures 9-2 through 9-4 and Box 9-1) can be recognized Box 9-1 Bundle-branch block: Identifying ECG features Rhythm: Rate: P waves: PR interval: QRS complex: Regular That of the underlying rhythm (usually sinus) Sinus Normal (0.12 to 0.20 second) Wide (0.12 second or greater) by a monitoring lead Differentiating between right and left bundle-branch block requires a 12-lead electrocardiogram (ECG) Figure 9-2 Normal sinus rhythm with bundle-branch block Rhythm: Rate: P waves: PR interval: QRS complex: Regular (off by squares) 60 to 65 beats/minute Sinus 0.16 to 0.20 second Figure 9-3 Normal sinus rhythm with bundle-branch block Regular 75 beats/minute Sinus P waves are notched, which could indicate left atrial enlargement 0.14 to 0.16 second 0.12 second A notched QRS complex is a common pattern with right bundle-branch block Rhythm: Rate: P waves: PR interval: QRS complex: Comment: 0.12 to 0.14 second ECG workout_Chap09.indd 198 4/28/2011 5:41:16 AM Premature ventricular contractions Figure 9.4 Rhythm: Rate: P waves: PR interval: QRS complex: 199 Atrial fibrillation with bundle-branch block Irregular 70 beats/minute Fibrillatory waves present Not measurable 0.14 to 0.16 second Right bundle-branch block (RBBB) may be present in healthy individuals with no apparent underlying heart disease, but more commonly occurs in the presence of coronary artery disease (the most common cause) RBBB may be temporary or chronic Occasionally, RBBB may appear only when the heart rate exceeds a certain critical level (rate-related BBB) Common causes include anteroseptal myocardial infarction (MI), pulmonary embolism, congestive heart failure, pericarditis, hypertensive heart disease, cardiomyopathy, congenital RBBB, and degenerative disease of the electrical conduction system Left bundle-branch block (LBBB) is rarely seen in individuals with healthy hearts It appears most commonly in elderly individuals with diseased hearts LBBB may be cycles temporary or chronic, and may be rate-related The most common cause is hypertensive heart disease Other causes are the same as with RBBB Specific treatment is usually not indicated for a bundle-branch block Cardiac pacing may be indicated if the bundle-branch block develops as a result of acute MI or in the presence of AV block Premature ventricular contractions A premature ventricular contraction (PVC) (Figures 9-5 through 9-14 and Box 9-2) is a premature, ectopic impulse that arises below the bundle of His in the ventricles PVCs compensatory pause PVC Figure 9-5 Rhythm: Rate: P waves: PR interval: QRS complex: Comment: ECG workout_Chap09.indd 199 Normal sinus rhythm with one premature ventricular contraction Basic rhythm regular; irregular with PVC Basic rhythm rate 79 beats/minute Sinus P waves with basic rhythm 0.16 to 0.20 second (basic rhythm) 0.08 to 0.10 second (basic rhythm); 0.14 to 0.16 second (PVC) The interval from the beat preceding the PVC to the beat following the PVC is equal to two cardiac cycles and represents a full compensatory pause 4/28/2011 5:41:18 AM 200 Ventricular arrhythmias and bundle-branch block A B Figure 9-6 Sinus P waves occurring before and after premature ventricular contractions (PVCs) The sinus P waves of the underlying rhythm can be seen just before the PVC in example A and after the PVC in the ST segment in example B These P waves are associated with the underlying rhythm (not the PVC) and usually are hidden within the wide QRS of the premature ventricular contraction Example A: Normal sinus rhythm with first-degree AV block and one PVC Example B: Sinus arrhythmia with bundle-branch block and one PVC Figure 9-7 Bigeminal premature ventricular contractions ECG workout_Chap09.indd 200 4/28/2011 5:41:19 AM Premature ventricular contractions 201 Figure 9-8 Trigeminal premature ventricular contractions Figure 9-9 Quadrigeminal premature ventricular contractions Figure 9-10 Paired premature ventricular contractions occur as a result of reentry in the ventricles, enhanced automaticity of a focus in the ventricles, or triggered activity occurring during ventricular repolarization PVCs have the following characteristics: Ⅲ The QRS is premature Ⅲ A P wave isn’t associated with the PVC Normally the P wave of the underlying rhythm (usually sinus) is obscured within the PVC, but sometimes it appears just before or after the PVC in the ST segment or T wave (see Figure 9-6) ECG workout_Chap09.indd 201 Ⅲ The QRS is wide (0.12 second or greater) and the morphology is different from the QRS complexes of the underlying rhythm Ⅲ The ST segment and T wave slope in the opposite direction from the main QRS deflection (if the ectopic QRS complex is predominantly negative, the ST segment is usually elevated and the T waves positive; if the ectopic QRS complex is predominantly positive, the ST segment is usually depressed and the T wave negative) 4/28/2011 5:41:20 AM 202 Ventricular arrhythmias and bundle-branch block Ⅲ The pause associated with the PVC is usually compensatory (the measurement from the beat before the PVC to the beat after the PVC is equal to two R-R intervals of the underlying rhythm, Figure 9-5) The underlying rhythm must be regular to determine a compensatory pause PVCs may occur in various patterns They may appear as a single beat (Figure 9-5), every other beat (bigeminal pattern, Figure 9-7), every third beat (trigeminal pattern, Figure 9-8), every fourth beat (quadrigeminal pattern, Figure 9-9), in pairs (also called couplets, Figure 9-10), or in runs (Figure 9-11) A run of three or more consecutive PVCs constitutes a rhythm The rate will determine which rhythm is present (idioventricular rhythm, accelerated idioventricular rhythm, or VT) PVCs that look the same in the same lead are called unifocal PVCs These PVCs originate from a single ectopic focus in the ventricles PVCs that appear different from one another in the same lead are called multifocal PVCs (Figure 9-12) These PVCs usually originate from different ectopic sites, but sometimes may fire from a single site and are Figure 9-11 Run of premature ventricular contractions (a burst of ventricular tachycardia) Figure 9-12 Multifocal premature ventricular contractions Box 9-2 Premature ventricular contraction (PVC): Identifying ECG features Rhythm: Rate: P waves: Figure 9-13 Interpolated premature ventricular contraction ECG workout_Chap09.indd 202 Underlying rhythm usually regular; irregular with PVC That of underlying rhythm (usually sinus) None associated with PVC; P waves associated with the underlying sinus rhythm can occasionally be seen just before the PVC or after the PVC in the ST segment or T wave; usually these P waves are hidden in the QRS complex PR interval: Not measurable QRS complex: Premature QRS complex; wide (0.12 second or greater) 4/28/2011 5:41:22 AM Premature ventricular contractions 203 Figure 9-14 R-on-T premature ventricular contraction conducted along different routes in the ventricles, resulting in a QRS that differs in morphology in the same lead A PVC sandwiched between two normally conducted sinus beats, without greatly disturbing the regularity of the underlying rhythm, is called an interpolated PVC (Figure 9-13) The compensatory pause, usually associated with the PVC, is absent R-on-T PVC (Figure 9-14) is a term used to describe a PVC which falls on the down slope of the preceding T wave This period corresponds to the relative refractory period of ventricular repolarization when the myocardium is in its most vulnerable state electrically During this period, the myocardial cells have repolarized enough to respond to a strong stimulus Stimulation of the ventricle at this time may precipitate repetitive ventricular contractions, resulting in VT or fibrillation PVCs are among the most commonly seen arrhythmias PVCs may occur in individuals with a healthy heart, but are more common in people with coronary heart disease PVCs are commonly caused by an increase in sympathetic tone from emotional stress; ingestion of substances such as alcohol, caffeine, or tobacco; mitral valve prolapse, myocardial ischemia or infarction; cardiomyopathy; congestive heart failure; hypoxia; electrolyte imbalances (especially hypokalemia); drug effects (digitalis, epinephrine, norepinephrine); as a reperfusion arrhythmia after thrombolytic therapy or angioplasty; or following insertion of invasive catheters into the heart, such as pacing leads or a pulmonary artery catheter Treatment of PVCs depends on the cause, the patient’s symptoms, and the clinical setting Because occasional PVCs are a normal finding in healthy individuals, no treatment may be indicated, especially if the person is asymptomatic Initially, a search should be made for possible reversible causes (such as oxygen for hypoxia; replacement of electrolytes; diuretics for heart failure; elimination of certain drugs; avoidance of alcohol, caffeine, or tobacco; and administration of antianxiety if indicated) Significant PVCs (more than per minute, multifocal PVCs, paired PVCs, R-on-T PVCs, or PVCs in runs of or more) should be treated with an antiarrhythmic medication, especially in the setting of acute MI or following cardiac surgery because of the increased risk of VT and VF in this setting On some occasions a ventricular beat may occur late instead of early A late ectopic ventricular beat usually occurs after a pause in the underlying rhythm in which the dominant pacemaker (usually the sinus node) fails to initiate an impulse If the ventricles are not activated by the sinus node, atria, or AV junction within a certain period of time, a focus in the ventricles may “escape” and pace the heart These are called ventricular escape beats (Figure 9-15) The ventricular escape beat is a protective mechanism, protecting the heart from slow rates, and no treatment is required Figure 9-15 Ventricular escape beat ECG workout_Chap09.indd 203 4/28/2011 5:41:24 AM 204 Ventricular arrhythmias and bundle-branch block Ventricular tachycardia Ventricular tachycardia (VT) (Figures 9-16 through 9-20 and Box 9-3) is an arrhythmia originating in an ectopic focus in the ventricles discharging impulses at a rate of 140 to 250 beats per minute VT is most likely due to reentry in the ventricles, but can also be caused by enhanced automaticity of a focus in the ventricles or to triggered activity occurring during ventricular repolarization VT occurs as a series of wide QRS complexes seen in short runs or as a continuous rhythm Because of the ventricular origin of the impulse, no P waves are produced The rhythm is usually regular, but may be slightly irregular The Box 9-3 Ventricular tachycardia (VT): Identifying ECG features Rhythm: Rate: P waves: PR interval: QRS complex: Regular; can be slightly irregular 140 to 250 beats/minute No P waves are associated with VT Not measurable Wide (0.12 second or greater) Figure 9-16 Ventricular tachycardia Rhythm: Rate: P waves: PR interval: QRS complex: Regular 150 beats/minute None identified Not measurable 0.14 to 0.16 second Figure 9-17 Ventricular flutter Rhythm: Rate: P waves: PR interval: QRS complex: Comment: Regular 375 beats/minute Not seen Not measurable 0.12 to 0.14 second Ventricular flutter is a form of ventricular tachycardia The ventricular rate is so fast the QRS complexes have a sawtooth appearance ECG workout_Chap09.indd 204 4/28/2011 5:41:25 AM Ventricular tachycardia 205 Figure 9-18 Atrial fibrillation with a burst of ventricular tachycardia (VT) Rhythm: Rate: P waves: PR interval: QRS complex: Basic rhythm irregular; VT regular 160 beats/minute (basic rhythm); 250 beats/minute (VT) Fibrillation waves in basic rhythm; none with VT Not measurable 0.08 to 0.10 second (basic rhythm); 0.12 second (VT) Figure 9-19 Ventricular tachycardia (torsade de pointes) Rhythm: Rate: P waves: PR interval: QRS complex: Comment: Regular 250 beats/minute None identified Not measurable 0.12 to 0.22 second (some much wider than others) This type of ventricular tachycardia is called torsade de pointes (twisting of the points) The QRS changes from negative to positive polarity and appears to twist around the isoelectric line It is associated with a prolonged QT interval and is refractory to antiarrhythmics IV magnesium or overdrive pacing has been successful in the treatment of this rhythm Electrical shock Figure 9-20 Electrical cardioversion of ventricular tachycardia to sinus rhythm ECG workout_Chap09.indd 205 4/28/2011 5:41:26 AM 206 Ventricular arrhythmias and bundle-branch block ST segment and T wave slope in the opposite direction from the main QRS deflection When the QRS complexes are of the same morphology in the same lead, the rhythm is termed monomorphic VT When the QRS complexes differ in morphology in the same lead, the VT is called polymorphic VT VT may occasionally occur at rates greater than 250 beats/ minute At such extreme rates the QRS complexes appear sawtooth in appearance and the rhythm is commonly referred to as ventricular flutter (Figure 9-17) Ventricular flutter is so rapid that there is virtually no cardiac output Ventricular flutter is often a precursor to ventricular fibrillation VT usually occurs in patients with underlying heart disease It may be preceded by significant PVCs (more than per minute, paired PVCs, multifocal PVCs), but often occurs without preexisting or precipitating PVCs The most common cause of sustained VT is coronary artery disease with prior MI Other causes include myocardial ischemia, acute MI, cardiomyopathy, congestive heart failure, mitral valve prolapse, valvular heart disease, digitalis toxicity, electrolyte imbalances (especially hypokalemia and hypomagnesemia), myocardial contusion, mechanical stimulation of the endocardium by a pacing catheter or pulmonary artery catheter, as an effect of reperfusion following thrombolytic therapy or angioplasty, and drugs that increase sympathetic tone (epinephrine, norepinephrine, dopamine) Certain medications or conditions may prolong the QT interval, causing the ventricles to be particularly vulnerable to a type of polymorphic VT called torsade de pointes (Figure 9-19) When VT lasts for less than 30 seconds it is called nonsustained VT VT occurring in short runs of three or more consecutive PVCs at a rate of 140 to 250 beats per minute is considered a “run” or “burst” of nonsustained VT (Figures 9-11 and 9-18) Nonsustained VT, unless frequent, usually doesn’t cause symptoms, but it can progress into sustained VT When VT lasts longer than 30 seconds, it is considered sustained VT Sustained VT is a life threatening arrhythmia for two major reasons: The rapid ventricular rate and loss of atrial kick reduce cardiac output This reduction in cardiac output often compounds the already low cardiac output frequently seen in the diseased hearts in which VT tends to occur The rhythm may degenerate into VF or asystole Treatment is based on the patient’s presentation An “unstable” patient refers to an individual who presents with symptoms such as hypotension, chest pain, shortness of breath, signs of decreased perfusion (cool, clammy skin; peripheral cyanosis; decreased level of consciousness; or a decrease in urine output) A “stable” patient refers to an individual with normal blood pressure, no chest pain, and no shortness of breath or signs of decreased perfusion As part of the initial assessment you should check for a pulse If there is not a pulse (pulseless VT), the rhythm must be treated as VF If there is a pulse, protocols for stable VT and unstable VT are followed ECG workout_Chap09.indd 206 Treatment protocols: Stable monomorphic VT with pulse Ⅲ Amiodarone (150 mg in 100 mL D5W) is given as an intravenous piggy-back (IVPB) bolus over 10 minutes An additional 150 mg IVPB bolus dose can be repeated in 10 minutes for resistant VT Once the rhythm converts to a stable rhythm, an amiodarone maintenance infusion should be started to prevent reoccurrence of VT The amiodarone maintenance infusion (900 mg in 500 mL D5W in a glass bottle) is started at mg per minute for hours, then decreased to 0.5 mg per minute for 18 hours The total dose of amiodarone (IVPB bolus doses plus maintenance infusion) should not exceed 2.2 g in 24 hours Oral amiodarone can be started once the maintenance infusion is completed Elimination of the drug from the body is extremely long (half-life lasts up to 40 days) Ⅲ If the rhythm is unresponsive to amiodarone, sedate the patient and perform synchronized cardioversion beginning at 100 joules biphasic energy dose, increasing in a stepwise fashion with subsequent attempts Some physicians prefer to skip drug therapy and go directly to synchronized cardioversion Figure 9-20 shows cardioversion of VT to sinus rhythm Treatment protocols: Unstable monomorphic VT with pulse Ⅲ Sedate the patient (if conscious) Ⅲ Convert the rhythm using synchronized cardioversion beginning at 100 joules biphasic energy dose, increasing in stepwise fashion with subsequent attempts Once cardioversion has converted the rhythm, a maintenance infusion of amiodarone is usually started at mg per minute for hours, then decreased to 0.5 mg per minute for 18 hours, followed by oral amiodarone once the maintenance infusion is completed Treatment of chronic, recurrent VT usually includes therapy with an oral antiarrhythmic Patients who are refractory to a pharmacologic approach may require further evaluation, which could include specialized electrophysiologic testing and endocardial mapping with long-term options including the use of an implantable cardioverter defibrillator (ICD) or reentry circuit ablation The ICD is a surgically implanted device developed to deliver an electric shock directly to the heart during a life-threatening tachycardia Ablation (destruction) of the reentry circuit involves delivering short pulses of radiofrequency current through an intracardiac catheter It produces a small burn that effectively blocks the part of the circuit supporting the reentrant-type wave Torsade de pointes ventricular tachycardia Torsade de pointes (TdP) (Figure 9-19) is a form of polymorphic VT This name is derived from a French term meaning “twisting of the points,” which describes a QRS complex that changes polarity (from negative to positive 4/28/2011 5:41:29 AM 28 29 30 ECG workout_Flash cards.indd 397 4/29/2011 7:15:22 PM 28 Answer: Normal sinus rhythm with first-degree AV block First-degree AV block: Identifying ECG features Rhythm: Usually regular Rate: That of the underlying sinus rhythm P waves: Sinus; one P wave to each QRS complex PR interval: Prolonged (greater than 0.20 second); remains consistent QRS complex: Normal (0.10 second or less) 29 Answer: Second-degree AV block, Mobitz I Mobitz I: Identifying ECG features Rhythm: Atrial: Regular Ventricular: Irregular Rate: Atrial: That of underlying rhythm Ventricular: Depends on number of impulses conducted through AV node; will be less than atrial rate P waves: Sinus PR interval: Varies; progressively lengthens until a P wave isn’t conducted (P wave appears without QRS complex); a pause follows the dropped QRS complex QRS complex: Normal (0.10 second or less) 30 Answer: Second-degree AV block, Mobitz I Mobitz I: Identifying ECG features Rhythm: Atrial: Regular Ventricular: Irregular Rate: Atrial: That of underlying rhythm Ventricular: Depends on number of impulses conducted through AV node; will be less than atrial rate P waves: Sinus PR interval: Varies; progressively lengthens until a P wave isn’t conducted (P wave appears without QRS complex); a pause follows the dropped QRS complex QRS complex: Normal (0.10 second or less) ECG workout_Flash cards.indd 398 4/29/2011 7:15:24 PM 31 32 33 ECG workout_Flash cards.indd 399 4/29/2011 7:15:24 PM 31 Answer: Second-degree AV block, Mobitz II with 2:1 and 3:1 AV conduction Mobitz II: Identifying ECG features Rhythm: Atrial: Regular Ventricular: Usually regular; may be irregular if AV conduction ratios vary Rate: Atrial: That of underlying rhythm Ventricular: Depends on number of impulses conducted through AV node; will be less than atrial rate P waves: Sinus; two or three P waves (sometimes more) before each QRS complex PR interval: Normal or prolonged; remains consistent QRS complex: Normal duration if block at bundle of His; wide if block in bundle branches 32 Answer: Second-degree AV block, Mobitz II with 3:1 AV conduction (one P wave hidden on top of T wave) Mobitz II: Identifying ECG features Rhythm: Atrial: Regular Ventricular: Usually regular; may be irregular if AV conduction ratios vary Rate: Atrial: That of underlying rhythm Ventricular: Depends on number of impulses conducted through AV node; will be less than atrial rate P waves: Sinus; two or three P waves (sometimes more) before each QRS complex PR interval: Normal or prolonged; remains consistent QRS complex: Normal duration if block at level of bundle of His; wide if block in bundle branches 33 Answer: Third-degree AV block Third-degree AV block: Identifying ECG features Rhythm: Atrial: Regular Ventricular: Regular Rate: Atrial: That of underlying sinus rhythm Ventricular: 40 to 60 beats/minute if paced by AV junction; 30 to 40 beats/minute (sometimes less) if paced by the ventricles; rate will be less than the atrial rate P waves: Sinus P waves with no consistent relationship to the QRS complex; P waves found hidden in QRS complexes, ST segments, and T waves PR interval: Varies (is not consistent) QRS complex: Normal duration if block at level of AV node or bundle of His; wide if block in bundle branches ECG workout_Flash cards.indd 400 4/29/2011 7:15:27 PM 34 35 36 ECG workout_Flash cards.indd 401 4/29/2011 7:15:27 PM 34 Answer: Third-degree AV block Third-degree AV block: Identifying ECG features Rhythm: Atrial: Regular Ventricular: Regular Rate: Atrial: That of underlying sinus rhythm Ventricular: 40 to 60 beats/minute if paced by AV junction; 30 to 40 beats/minute (sometimes less) if paced by the ventricles; rate will be less than the atrial rate P waves: Sinus P waves with no consistent relationship to the QRS complex; P waves found hidden in QRS complexes, ST segments, and T waves PR interval: Varies (is not consistent) QRS complex: Normal duration if block at level of AV node or bundle of His; wide if block in bundle branches 35 Answer: Normal sinus rhythm with bundle-branch block Bundle-branch block: Identifying ECG features Rhythm: Usually regular Rate: That of underlying rhythm (usually sinus) P waves: Sinus PR interval: Normal (0.12 to 0.20 second) QRS complex: Wide (0.12 second or greater) 36 Answer: Normal sinus rhythm with bundle-branch block Bundle-branch block: Identifying ECG features Rhythm: Usually regular Rate: That of underlying rhythm (usually sinus) P waves: Sinus PR interval: Normal (0.12 to 0.20 second) QRS complex: Wide (0.12 second or greater) ECG workout_Flash cards.indd 402 4/29/2011 7:15:29 PM 37 38 39 ECG workout_Flash cards.indd 403 4/29/2011 7:15:29 PM 37 Answer: Normal sinus rhythm with two multifocal PVCs Premature ventricular contraction: Identifying ECG features Rhythm: Underlying rhythm usually regular; irregular with PVC Rate: That of underlying rhythm P waves: None associated with PVC PR interval: Not measurable QRS complex: Premature, wide QRS (0.12 second or greater) with ST segment and T wave sloping opposite the main QRS deflection; followed by a pause 38 Answer: Normal sinus rhythm with two unifocal PVCs Premature ventricular contraction: Identifying ECG features Rhythm: Underlying rhythm usually regular; irregular with PVC Rate: That of underlying rhythm P waves: None associated with PVC PR interval: Not measurable QRS complex: Premature, wide QRS (0.12 second or greater) with ST segment and T wave sloping opposite the main QRS deflection; followed by a pause 39 Answer: Ventricular tachycardia Ventricular tachycardia: Identifying ECG features Rhythm: Usually regular (may be slightly irregular) Rate: 140 to 250 beats/minute P waves: No associated P waves PR interval: Not measurable QRS complex: Wide (0.12 second or greater) with ST segments and T waves sloping opposite the main QRS deflection ECG workout_Flash cards.indd 404 4/29/2011 7:15:32 PM 40 41 42 ECG workout_Flash cards.indd 405 4/29/2011 7:15:32 PM 40 Answer: Ventricular tachycardia (torsade de pointes) Torsade de pointes: Identifying ECG features Rhythm: Usually regular (may be slightly irregular) Rate: 200 beats/minute or more P waves: None PR interval: Not measurable QRS complex: 0.12 second or greater (some much wider than others) 41 Answer: Normal sinus rhythm with 3-beat run of VT Ventricular tachycardia: Identifying ECG features Rhythm: Usually regular (may be slightly irregular) Rate: 140 to 250 beats/minute P waves: No associated P waves PR interval: Not measurable QRS complex: Wide (0.12 second or greater) with ST segments and T waves sloping opposite the main QRS deflection 42 Answer: Ventricular fibrillation (coarse deflections present) Ventricular fibrillation: Identifying ECG features Rhythm: None (P wave and QRS are absent) Rate: None (P wave and QRS are absent) P waves: Wavy, irregular deflection representative of ventricular quivering; deflections may be small (fine ventricular fibrillation) or coarse (coarse ventricular fibrillation) PR interval: Not measurable QRS complex: Absent ECG workout_Flash cards.indd 406 4/29/2011 7:15:34 PM 43 44 45 ECG workout_Flash cards.indd 407 4/29/2011 7:15:34 PM 43 Answer: Ventricular fibrillation (fine deflections present) Ventricular fibrillation: Identifying ECG features Rhythm: None (P wave and QRS are absent) Rate: None (P wave and QRS are absent) P waves: Wavy, irregular deflections representative of ventricular quivering; deflections may be small (fine ventricular fibrillation) or coarse (coarse ventricular fibrillation) PR interval: Not measurable QRS complex: Absent 44 Answer: Idioventricular rhythm Idioventricular rhythm: Identifying ECG features Rhythm: Regular Rate: 30 to 40 beats/minute (sometimes less) P waves: Absent PR interval: Not measurable QRS complex: Wide (0.12 second or greater) 45 Answer: Accelerated idioventricular rhythm Accelerated idioventricular rhythm: Identifying ECG features Rhythm: Regular Rate: 50 to 100 beats/minute P waves: Absent PR interval: Not measurable QRS complex: Wide (0.12 second or greater) ECG workout_Flash cards.indd 408 4/29/2011 7:15:35 PM 46 47 48 ECG workout_Flash cards.indd 409 4/29/2011 7:15:35 PM 46 Answer: Normal sinus rhythm with 3-beat run AIVR Accelerated idioventricular rhythm: Identifying ECG features Rhythm: Regular Rate: 50 to 100 beats/minute P wave: Absent PR interval: Not measurable QRS complex: Wide (0.12 second or greater) 47 Answer: Ventricular standstill (asystole) Ventricular standstill: Identifying ECG features Rhythm: Atrial: If waves present, will have atrial rhythm Ventricular: None; no QRS complexes are present Rate: Atrial: If P waves present, will have atrial rate Ventricular: None; no QRS complexes are present P waves: Tracing will show only P waves or a straight line PR interval: Not measurable QRS complex: Absent 48 Answer: Ventricular standstill (asystole) Ventricular standstill: Identifying ECG features Rhythm: Atrial: If P waves present, will have atrial rhythm Ventricular: None; no QRS complexes are present Rate: Atrial: If P waves present, will have atrial rate Ventricular: None; no QRS complexes are present P waves: Tracing will show only P waves or a straight line PR interval: Not measurable QRS complex: Absent ECG workout_Flash cards.indd 410 4/29/2011 7:15:37 PM Electrocardiographic conversion table for heart rate Number of small spaces 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Rate per minute 300 250 214 188 167 150 136 125 115 107 100 94 88 84 79 75 72 68 65 63 60 Number of small spaces 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 Rate per minute 58 56 54 52 50 48 47 45 44 43 42 41 40 39 38 37 36 35 34 33 33 Number of small spaces 47 48 49 50 52 54 56 58 60 62 64 68 72 76 80 84 88 92 98 104 112 Rate per minute 32 31 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 ... Rate: P waves: PR interval: QRS complex: ECG workout_Chap09.indd 20 9 Regular 41 beats/minute Absent Not measurable 0 .22 to 0 .24 second 4 /28 /20 11 5:41:30 AM 21 0 Ventricular arrhythmias and bundle-branch... _ ECG workout_Chap09.indd 22 0 4 /28 /20 11 5:41: 42 AM Rhythm strip practice: Ventricular arrhythmias and bundle-branch block 22 1 Strip 9 -22 Rhythm: Rate:... _ ECG workout_Chap09.indd 22 1 4 /28 /20 11 5:41:44 AM 22 2 Ventricular arrhythmias and bundle-branch block Strip 9 -25 Rhythm: Rate: P wave: PR interval: